The present invention relates particularly to truck-carried ramps which stow within the frame of the vehicle below the cargo carrying body of the motorized truck, and are adaptable to be removed rearwardly to a position in which the ramp assumes a tilted position resting on the ground and connected to the vehicle adjacent the floor of the cargo compartment so as to be useable for cargo loading and unloading purposes. Typically, support arms have been pivotally attached beneath the front ends of such ramps and and the front ends of the arms have been pivotally connected to the vehicle frame within the ramp storage chamber. These support arms have supported the front end of the ramp when it is initially extended from the vehicle until such time as the front end could be raised vertically and pulled rearwardly to hook into openings provided in the vehicle frame which retained the front end of the ramp in a raised position in which the floor of the front end of the ramp was substantially at the level of the floor of the cargo compartment of the truck. In this operatively deployed position of the ramp, hand trucks carrying considerable loads easily transfer between the ramp and the floor of the cargo container.
Applicant's assignee has marketed retractable underbody truck ramps of this type for a number of years and the present invention is directed to certain new and useful improvements which have been made in such truck-ramp structures. Applicant's assignee has manufactured a range of ramps of differing length and weight for use with cargo-carrying trucks of varying size and floor level. For example, applicant's assignee has manufactured and marketed ramps ranging from 10 to 16 feet in length, and weighing between 80 and 140 pounds, in conjunction with appropriate track assemblies forming ramp storage chambers which are adapted to be welded to the truck body frame in a position to receive both the stowed ramp floors and the front end support arms which are folded up to the ramp floors to also be received in the longitudinally extending ramp storage chambers. To provide attachment devices at a proper level to secure the front end of the ramp when it is removed from the storage chamber and raised, notches have been cut in the rear apron of the truck body at cargo floor level to receive hooks provided on the front end of the ramp. Rollers have been mounted at the front and rear ends of the ramp in a position to support the ramp above storage frame members forming tracks on which the rollers move, as the ramps and arms are pushed telescopically into the ramp stowing chamber beneath the truck body floor. Because cargo truck specifications vary with the manufacturer of the cargo truck, applicant's assignee's ramps had to be designed to accommodate to trucks having variable vertical distances between the storage chambers and beds of the truck, and to truck bodies having aprons which projected different distances.
With ramps of this prior art construction, a truck driver, typically making 10 to 12 deliveries per day, must exert considerable physical force to first remove the ramp from its storage chamber, and then raise the 60 to 80 pounds of front end dead weight of the ramp and pull it forewardly to attach it to the apron of the truck bed, each time a delivery is to be made. As a result of this, and particularly toward the end of a day when the truck operator may be tired and rushed, many drivers have simply pulled the truck ramp from the stowing chamber and sought to operate it without attaching its front end to the apron of the truck body floor. While operation in this manner avoids the physical exertion required to raise the front end of the ramp and simultaneously pull it forewardly, while its rearmost end is in engagement with, for example, a very rough concrete surface creating considerable friction, the practice is regarded as unsafe and capable of causing injury to the operator of the hand truck which is used to load and unload the vehicle, as well as to the cargo being transferred. The reason for this is that there will be a considerable drop between the floor of the cargo truck and the upper end of a ramp which has not been raised to the level of the truck bed and attached thereto. When cargo is being unloaded from such a truck bed by hand truck and the wheels of the hand truck fall from the bed to the upper end of the ramp, injuries to the back of the hand truck operator who normally is the driver of the truck, can occur and, of course, cargo being carried on the hand truck may fall off the hand truck and drop a considerable distance to the ground. The practice is also very hard on hand trucks, and can materially shorten their useful lives.